1. Field of the Invention
The invention relates to the field of detection of impurities in a fluid. Specifically, the invention relates to an apparatus and method that facilitates the detection of minimal quantities of impurities in hydrogen fuel through concentration of the impurities by a known amount and subsequent measurement of the concentrated impurities. When coupled with an appropriate detector or sensor, the device can provide quantitative analysis (or concentrations) of the impurities in the original sample gas.
2. Background of the Invention
Fuel cell and other hydrogen fueled vehicles are slated for commercial deployment in the US and around the world. A number of demonstration hydrogen refueling centers have been set up around the US. Several teams of vehicle manufacturers and fuel suppliers have worked with state and federal government1,2 in the demonstration of hydrogen refueling centers where the hydrogen is dispensed at the nozzle at elevated pressure (5,000-10,000 psig) into a vehicle's hydrogen storage tanks. Since fuel cells are very sensitive to gases like carbon monoxide, hydrogen sulfide, ammonia, etc., the fuel supplier must ensure that the concentrations of these species are limited to suggested guidelines. Examples of these guideline values suggested by the Society of Automotive Engineers (SAE) are shown in Table 1, and show that the limits on CO, NH3 and sulfur are extremely low and that they are at, or very close to, the detection limits of standardized analytical methods.
TABLE 1SAE suggested guideline values for the maximumallowable concentrations for impurities inhydrogen for fuel cell vehicles.Hydrogen, minimum99.97%Impurities & LimitsMaximum(Excluding helium, must be <100 ppm)Helium (He)300ppmNitrogen (N2) + Argon (Ar)100ppmTotal Hydrocarbons (HC) (C1 basis)2ppmCarbon Dioxide (CO2)2ppmCarbon Monoxide (CO)0.2ppmAmmonia (NH3)0.1ppmSulfur (S, as H2S, COS, etc.)0.004ppm                H2 suppliers (stations) will need to meet these specifications and certify the purity of the product they dispense.        
Hydrogen-generation plants currently at the demonstration refueling centers operate at conservative operating conditions to ensure the desired quality of hydrogen. The gas dispensed to the vehicles is periodically sampled and analyzed using customized analytical methods and sophisticated equipments. Organizations such as the ASTM are developing new standardized methods for the analysis of hydrogen for fuel cells.
Meanwhile, the current practice is to harvest samples periodically and send the samples to analytical laboratories, where the fluids are analyzed. State of the art instrumentation is required, such as, for example, a gas chromatograph fitted with a pulse discharged helium ionization detector (GC/PDHID) to analyze for carbon monoxide at concentrations of 0.2 parts per million or lower, or a gas chromatograph fitted with a sulfur chemiluminescence detector (GC/SCD) to analyze for total sulfur species. These sensitive instruments are expensive, and they require considerable laboratory time of skilled analytical chemists.
The high cost of these analyses can be borne by the demonstration projects because of the large intervals between gas samples. However, with the larger deployment of fuel cell vehicles and the anticipated growth in the refueling infrastructure in the years ahead, refueling stations will have to conduct more frequent and rapid analysis and/or monitoring of the key species, using simpler and inexpensive technologies. Some of the key factors that necessitate the development of new analytical technology for analysis of hydrogen are:                Standardized methods for analysis of the trace species have not been defined and validated.        Current methods require the use of expensive equipment that can cost in excess of $100,000 per unit and are not suited for on-site analysis. Indeed, the pressures at which hydrogen is to be stored at refueling stations is much higher than state of the art current hydrogen sampling methods which operate at no more than atmospheric pressures, and usually less.        Current methods require considerable time and skilled operators.        Current analytical methods can add 4-10 cents/kg to the cost of hydrogen.        
A need exists in the art for an in-situ apparatus and method to determine contaminant levels in hydrogen fuels. The apparatus and method should not require costly analytical tools or elaborate protocol so as to allow their use by minimally trained personnel at vehicle refilling stations. The apparatus and method should be operable at hydrogen gas pressures much higher than atmospheric pressure, and typically operable at pressures at which hydrogen gas is commercially stored.